The bedrock of Marine tradition is a long-ago era when buff, male and mostly white combat Marines launched amphibious early-morning assaults on enemy beaches armed with M1 rifles and Ka-Bar knives. Today’s far less homogeneous troops roll into battle in armored Humvees or tanks, with sophisticated high-powered weaponry and thermal-imaging goggles. Many never leave their base at all, waging war remotely while operating a joystick or writing code. In many ways, the Marines have become indistinguishable from the Army.

Adapting to these harsh truths hasn’t been easy for the corps, whose current and former officials, with some exceptions, were reluctant to speak openly about these challenges except on condition of anonymity. ‘‘The Marines have a purpose, and it’s a militant purpose,’’ one senior officer says. ‘‘We are an organization grounded on the physical, but wars are not as physical anymore. The character of war has evolved a lot from the early 20th century. The question is: Has our force evolved? I don’t think it has.’’